1) Field of the Invention
The present invention relates to a rubber composition for magnetic encoder, and more particularly to a rubber composition for magnetic encoder capable of giving molding product with improved heat resistance, water resistance, saline water resistance, etc.
2) Related Art
Rubber magnets for sensors are used in magnetic encoder at encoder positions of speed sensors, etc. NBR is usually used as a rubber component of rubber magnets in wheel speed sensors, but when applied to positions of driving systems around engines, NBR is exposed to high temperature situations, e.g. about 130°–about 170° C., and thus NBR having an upper limit heat-resistant temperature of about 120° C. cannot withstand such high temperature situations.
On the other hand, rubbers capable of withstanding such high temperature situations of about 130°–about 170° C. include, for example, silicone rubber, fluororubber, etc., but silicone rubber has an oil resistance problem, whereas in the case of fluororubber the rubber flexibility is considerably lost when magnetic powder is filled therein in a high mixing proportion, so the mixing proportion of magnetic powder is limited, that is, there is such a problem that a high magnetic force is hard to obtain.
When wheel speed sensors are applied to positions at an underbody portion of a car including suspensions, wheels, etc., water resistance and saline water resistance properties are further required for the rubber of the rubber magnets, but NBR fails to satisfy these requirements and thus further improvements have been desired.